The present invention relates to an integrated circuit/packet switching system which can handle both circuit- and packet-switching signals in an unified procedure.
As well known in the art, there are available a circuit switching system and a packet switching system.
The two switching techniques have their own merits and demerits and find different fields of applications. The circuit switching technique guarantees communication channels of given bandwidths or speeds from the start till the end of each message (or call) with a minimum of delay time and without delay time variation. Its advantages thus can be enjoyed when it is applied to data communication where data in transmitted in large quantities and continuously such as voice communication, facsimile and file transfer services. A disadvantage is that high system efficiency cannot be retained for conversation type communication services where a small amount of data occurs intermittently such as TSS (time sharing system) and information request services. The packet switching technique, on the other hand, can efficiently multiplex information by once storing information in buffer and then queuing channels. This procedure is thus suited to conversation type communication services. However, the delay time is large compared to the case of circuit switching, and also there are delay time variations. Therefore, this method is not suited for voice communication and like services.
At present, different switching systems are adopted for different kinds of services. That is, independent communication networks adopting switching systems suited for specific service categories are constructed. For example, voice communication service network (adopting circuit switching function), telex network (adopting circuit switching function), circuit switched data network and packet switched data network are constructed independently. This philosophy has an advantage that each network can be optimized for its specific service. Disadvantageously, however, there are plural independent networks, which are slightly different in architecture or performance but closely resemble one another in general aspect, partly overlap for a specified performance, leading to complicated network operation and control. In addition, since the individual networks are comparatively small in scale, a so-called aggregation effect, is impaired, leading to low efficiency of the communication facility. Besides, different networks for different service categories will present many problems when it is intended to integrate a plurality of different services to provide a composite service system. Moreover, in order to realize a novel service, it is necessary to establish a new network. Accordingly, if the circuit and packet switching functions are integrated on a single network which is suited for an extremely wide variety of communication services, great advantages will be enjoyed. To this end, it is indispensable to realize an integrated circuit/packet transmission system and integrated circuit/packed switching system in the network.
A heretofore proposed integrated circuit/packet switch module has an architecture as shown in FIG. 1. Referring to FIG. 1, discriminators 11 discriminate between circuit and packet switched calls arriving from transmission lines 10 and transmit the circuit-switched calls to a circuit switching section 13 via links 12 while transmitting the packet-switched calls to a packet switching section 15 via links 14. The circuit switching section 13 and packet switching section 15 have conventional structures. These switching sections switch the respective circuit-switched and packet-switched calls back to the discriminators 11 via the links 12 and 14. The discriminators 11 send out both these calls to the corresponding transmission lines 10. The architecture of the discriminator 11 varies with the manner, in which circuit- and packet-switched calls are integrated on the lines 10. At any rate, the principle is to separate incoming circuit- and packet-switched calls from the lines or, conversely, sent out both the calls in an integrated form to the lines.
With the scheme of FIG. 1, however, although both the circuit switching and packet switching may be realized physically in the same switch module, the two are logically entirely not realy integrated but are distinct from one another. More specifically, the circuit switching section and packet switching section must be designed independently in compliance with the characteristics of the processed circuit- and packet-switched calls. Therefore, overlapped function and equipment still exist and the system efficiency is low, and the merits of the integration of circuit and packet switching functions noted above can be hardly obtained.
Meanwhile, there have been attempts to process both circuit- and packet-switched calls on the same network, e.g., in-house private networks and especially local area networks (LAN) which are recently attracting great interest. Therefore, it is conceivable to construct a speech path network of an exchange after local area networks. FIG. 2 shows an architecture, which comprises a plurality of modules (hereinafter referred to nodes) 20 each accommodating a number of user access lines and/or inter-office trunks and a plurality of loops 21 for inter-node network. Following the conventional local area network scheme, the individual loops 21 operate with a fixed cycle time frame format, as shown in FIG. 3. The frame contains a plurality of time slots. These time slots are split into those for circuit-switched calls and those for packet-switched calls. Each node receives and transmits circuit-switched calls using time slots alloted thereto and packet-switched calls using time slots alloted thereto. Each circuit-switched call is sent on the loops using the same time slots in each frame while the communication circuit is set up. On the other hand, each packet-switched call is sent on the basis of one of well-known time slot access algorisms (e.g., token passing method).
In this approach, if the time slot shares for circuit- and packet-switched call are fixed, idle time baskets for the call of one category cannot be used for a call of the other category, leading to reduced system efficiency. In addition, although the circuit switching and packet switching are physically integrated, the two are logically entirely distinct from one another. The technique thus does not substantially differ from the approach shown in FIG. 1, and the merits of the integration of circuit switching and packet switching cannot be obtained. A movable boundary system, in which the time slot shares are variable, can allot time slots according to the circuit- and packet-switched call traffic amounts to alleviate the system efficiency decrease due to loss. In this case, however, a control node is needed, which specifies the boundary by observing both call category trafic amounts. Or, where there is a control node, the function noted must be additionally provided thereon. However, instantaneous observation of the trafic is impossible, so that it is impossible to instantaneously vary the time slot shares to reduce the loss to zero. This inefficiency essentially arises from specifically alloting the time slots for circuit- and packet-switched calls.
There have been some proposals with an aim of real integration of both switching functions. One approach is to integrate all commuication services by the packet switching technique, the services including even voice and like services, for which the circuit switching technique has been thought to be suited. When applied to voice communication service, digitized voice information generated in a predetermined interval of time is assembled into a packet, which is transmitted to the destination by the conventional packet switching procedure. Each packet is provided with a header, which contains destination address, logical channel number and other control data. The packet is transmitted to the destination by reference to the header. In this case, the size of one packet must be sufficiently large to minimize the transmission efficiency decrease due to the header. Therefore, the delay time due to packet assembly time (i.e., time necessary for storing an amount of information corresponding to a packet having a predertermined size) is large for voice communication services. In addition, packets are once stored and set on after having succeeded in hunting idle channels. This means that the queuing time varies with packets of even the same channel message or call. Therefore, for voice communication or like services which require time transparency (a character that the delay time is constant), a receiving buffer for absorbing delay time variations is necessary, which further increases the delay time. In a network which covers a broad geometrical area so that a call from a source to a destination may be relayed by a number of excahnge offices, increased delay times in the individual offices may amount to a very large absolute delay time to cause an echo or deteriorate the message quality. In order to reduce delay time, it is necessary to reduce the packet assembly time by reducing the packet length and also reduce the capacity of the delay absorption buffer. Doing so, however, leads to transmission efficiency decrease and message quality deterioration due to packet loss.
Another approach is to adopt the circuit switching technique for integration of circuit- and packet-switched calls even for services, for which the packet switching technique is thought to be suited. An example of this approach is a fast circuit switching system. In this system, a circuit is set up for each of intermittently transmitted pieces of information of a call and is cleared down as soon as the transmission is over. This procedure can avoid channel holding overhead and improve the system efficiency. A significant point to this system is the fastness with which to set up and clear down the circuit. In a network covering a broad area, however, a communication circuit between a source and a destination must be set up and cleared down via a number of exchange offices, and it is actually extremely difficult to set the circuit set-up and clear-down time to be very small compared to the actual transmission period, during which the channel is occupied by the transmitted information. Efficiency decrease of the channel is thus inevitable. Further, in a heterogeneous traffic processing network covering a wide variety of bandwidth (or speed) services, such controls as securing necessary bandwidth or speed channels for each call over the entire route and assembling a plurality of secured unit bandwidth or unit speed channels into a call are independently required for each service category. The control involved thus is extremely complicated, leading to scale and complexity increase of the switching system hardware and software.
The drawbacks in the prior art discussed above are summarized as follows.
(1) Real integration of the circuit and packet switching functions lacks, so that the merits of the integration such as improved facility efficiency and unified operation and control cannot be obtained (in case of coexistent circuit/packet switching techniques).
(2) Delay time is large for circuit-switched channels such as voice services (in case of integration by packet switching technique).
(3) Time transparency lacks for circuit-switched channels such as voice services (in case of integration by packet switching technique).
(4) System efficiency is inferior for communication services wherein occurrence of transmission data is intermittent (in case of integration by circuit switching technique).
(5) Control of heterogeneous traffic networks is complicated (in case of integration by circuit switching technique).